Transglutaminase (hereinafter, referred to as "BTG") is an enzyme which catalyzes an acyl transfer reaction of a .gamma.-carboxyamide group of glutamine residue in a peptide chain.
BTG induces intramolecular or intermolecular formation of .epsilon.-(.gamma.-Gln)-Lys cross linking when an .epsilon.-amino group of a lysine residue in a protein molecule functions as an acyl receptor. Also, when water functions as an acyl receptor, this enzyme accelerates conversion of glutamine residues into glutamic acid residues by deamidation.
Because of its function to gel protein, BTG has been employed in the production of gelled food, gelled cosmetics, yogurt, gelatins, cheese and the like (JP-B-1-50382). (The term "JP-B" as used herein means an "examined Japanese patent publication".) This enzyme has also been employed in the production of thermally stable materials such as microcapsules, carriers of immobilized enzymes and the like.
BTG has been found in animals, for example, in the liver of guinea pigs (Connellan et al., Journal of Biological Chemistry, vol. 246, No. 4, pp. 1093-1098 (1971)) and in various organs and blood of mammals (Folk et al., Advances in Enzymology, vol. 38, pp. 109-191 (1973); and Folk et al., Advances in Protein Chemistry, vol. 31, pp. 1-133 (1977)), and its enzymological properties have been studied. In addition, a different type of BTG, which is independent of calcium (Ca.sup.2+) and is therefore different from the animal-derived BTG, has been found in various strains of the genus Streptoverticillium. Illustrative examples of these strains include Streptoverticillium griseocarneum IFO 12776, Streptoverticillium cinnamoneum sub sp. cinnamoneum IFO 12852, Streptoverticillium mobaraense IFO 13819 and other species (cf. JP-A-64-27471). (The term "JP-A" as used herein means an "unexamined published Japanese patent application".)
Since BTG is obtained from animals, micro-organisms and the like, there are many problems to be solved such as a low production yield and an expensive production cost.
As a result of extensive investigations to overcome these problems of the prior art, the inventors of the present invention have succeeded in isolating and purifying a DNA gene which encodes BTG and determining its base sequence. On the basis of these results, the present inventors have provided a method for producing BTG efficiently in a large quantity through expression of the DNA gene in microorganisms such as Escherichia coli using genetic engineering.